Water Rocket Forum

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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

I'm a mentor for a high school FIRST robotics and Electrothon team in the USA, and I'm getting them interested in water rocketry. We are considering a 2-stage record setting attempt at an event in June 2013. I suspect I'll have many rule questions in the future. First question: Safety rule II.2 states "The payload section is to be attached above all pressurized parts of the rocket and cannot contain any exposed metal parts." Does this mean that the payload section has to stay attached to a pressure vessel during flight? One idea was to built the second stage in a booster configuration. The payload section would be constructed from a short T8 or T12 tube and the second stage pressure vessel from two or three liter soda bottles. The boosters would fall away soon after the initial stage, leaving an aerodynamic T8 or T12 tube to finish the flight. (Think Saturn V with the Apollo program. How much did we launch, and how much did we get back!) This design also opens the interesting possibility of deploying the chute from the rear of the payload section instead of the front or side.

I'm a mentor for a high school FIRST robotics and Electrothon team in the USA, and I'm getting them interested in water rocketry. We are considering a 2-stage record setting attempt at an event in June 2013. I suspect I'll have many rule questions in the future. First question: Safety rule II.2 states "The payload section is to be attached above all pressurized parts of the rocket and cannot contain any exposed metal parts." Does this mean that the payload section has to stay attached to a pressure vessel during flight? One idea was to built the second stage in a booster configuration. The payload section would be constructed from a short T8 or T12 tube and the second stage pressure vessel from two or three liter soda bottles. The boosters would fall away soon after the initial stage, leaving an aerodynamic T8 or T12 tube to finish the flight. (Think Saturn V with the Apollo program. How much did we launch, and how much did we get back!) This design also opens the interesting possibility of deploying the chute from the rear of the payload section instead of the front or side.

Thanks in advance

Hello SeaWolf and welcome

To answer your question, no the payload bay does not need to stay attached. If it does detach or separate though it must use some form of recovery system to limit descent rate to the limit provided in the rules (see section III-1 and III-2 for recovery system rules and maximum descent rate).

This brings up another potential question so I will answer now.

If the payload bay separates at apogee the rocket would be considered a single stage but if the payload bay separated during the flight and was designed to "continue flying" (even if unpowered) the rocket would be considered "multi-stage" and would need to be entered in the multi-stage competition.

I'm a mentor for a high school FIRST robotics and Electrothon team in the USA, and I'm getting them interested in water rocketry. We are considering a 2-stage record setting attempt at an event in June 2013. I suspect I'll have many rule questions in the future. First question: Safety rule II.2 states "The payload section is to be attached above all pressurized parts of the rocket and cannot contain any exposed metal parts." Does this mean that the payload section has to stay attached to a pressure vessel during flight? One idea was to built the second stage in a booster configuration. The payload section would be constructed from a short T8 or T12 tube and the second stage pressure vessel from two or three liter soda bottles. The boosters would fall away soon after the initial stage, leaving an aerodynamic T8 or T12 tube to finish the flight. (Think Saturn V with the Apollo program. How much did we launch, and how much did we get back!) This design also opens the interesting possibility of deploying the chute from the rear of the payload section instead of the front or side.

Thanks in advance

Hello SeaWolf and welcome

To answer your question, no the payload bay does not need to stay attached. If it does detach or separate though it must use some form of recovery system to limit descent rate to the limit provided in the rules (see section III-1 and III-2 for recovery system rules and maximum descent rate).

This brings up another potential question so I will answer now.

If the payload bay separates at apogee the rocket would be considered a single stage but if the payload bay separated during the flight and was designed to "continue flying" (even if unpowered) the rocket would be considered "multi-stage" and would need to be entered in the multi-stage competition.

Well, that greatly simplifies things because it eliminates a second stage pressure coupler. To be clear, I don't need a second powered stage to classify for multi-stage. Having a single booster mechanically separate from the payload section once the thrust phase is complete is enough.

I'm a mentor for a high school FIRST robotics and Electrothon team in the USA, and I'm getting them interested in water rocketry. We are considering a 2-stage record setting attempt at an event in June 2013. I suspect I'll have many rule questions in the future. First question: Safety rule II.2 states "The payload section is to be attached above all pressurized parts of the rocket and cannot contain any exposed metal parts." Does this mean that the payload section has to stay attached to a pressure vessel during flight? One idea was to built the second stage in a booster configuration. The payload section would be constructed from a short T8 or T12 tube and the second stage pressure vessel from two or three liter soda bottles. The boosters would fall away soon after the initial stage, leaving an aerodynamic T8 or T12 tube to finish the flight. (Think Saturn V with the Apollo program. How much did we launch, and how much did we get back!) This design also opens the interesting possibility of deploying the chute from the rear of the payload section instead of the front or side.

Thanks in advance

Hello SeaWolf and welcome

To answer your question, no the payload bay does not need to stay attached. If it does detach or separate though it must use some form of recovery system to limit descent rate to the limit provided in the rules (see section III-1 and III-2 for recovery system rules and maximum descent rate).

This brings up another potential question so I will answer now.

If the payload bay separates at apogee the rocket would be considered a single stage but if the payload bay separated during the flight and was designed to "continue flying" (even if unpowered) the rocket would be considered "multi-stage" and would need to be entered in the multi-stage competition.

Well, that greatly simplifies things because it eliminates a second stage pressure coupler. To be clear, I don't need a second powered stage to classify for multi-stage. Having a single booster mechanically separate from the payload section once the thrust phase is complete is enough.

You are correct. You do not need a powered second stage for the rocket to be considered a multi stage. In the rocketry world this is called a "boosted dart".

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association